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Thursday, 28 February 2013

STRUCTURE OF HUMAN EYE 2

IMPORTANT POINTS

The retina ---contains numerous light sensitive cells which generate electrical signals which are sent to brain via optic nerve

Cornea---The transparent spherical membrane covering the front of the eye.

Iris--The coloured diaphragm between the cornea and lens.

Pupil ---The small hole in the iris.

Eye lens--- It is a transparent lens made of jelly like material.

Ciliary muscles--These muscles hold the lens in position.

Retina--The back surface of the eye.

Blind spot--The point at which the optic nerve leaves the eye. An image formed at this point is not sent to the brain.

Aqueous humour---A clear liquid region between the cornea and the lens.

Vitreous humour--The space between eye lens and retina is is filled with another liquid called Vitreous humour.

Persistence of vision--The image of an object seen persists on the retina for 1/16 second even after the removal of the object. This continuance of sensation of eye for some timed is called persistence of vision.

Colour blindness--It is said to occur when a person cannot distinguish between colours

Accomodation--The ability of the eye to focus both near and distant objects, by adjusting the focal length, is called the accommodation of the eye.

Far Point of the Eye--It is the farthest point at which the object can be seen clearly. For a normal eye, the far point lies at infinity.

Near point of the Eye-- It is the closest point at which an object can be seen clearly. For normal eye, the near point lies at 25 cm from the eye(least distance of distinct vision).